TIMING AND ORIGIN OF A MULTI-COMPONENT FLUID-RELATED REMAGNETIZATION IN FOLDED MISSISSIPPIAN CARBONATES IN THE SOUTHERN CANADIAN CORDILLERA, SE BRITISH COLUMBIA AND SW ALBERTA

Determining the timing and origin of fluid-related diagenetic events relative to orogenesis is crucial for understanding the interaction between thin skinned tectonics and diagenesis. In order to investigate this issue a combination of geochemical, petrographic and fluid inclusion analysis is needed to determine the nature of various diagenetic events and then paleomagnetic analysis can be used to date chemical remanent magnetizations (CRM’s) formed by these events. Two folds in Mississippian carbonates with abundant degraded hydrocarbons have been investigated in the Front Range of the Southern Canadian Cordillera in order to test for a link between fluid flow, deformation and a multi-component remagnetization. The characteristic remanent magnetization (ChRM) is contained in magnetite and is pretilting to early syntilting and was acquired in the Early to late Cretaceous. An intermediate temperature component is a late syntilting to post tilting Tertiary age remagnetization contained in pyrrhotite. Both components are pervasive throughout the host carbonate and are interpreted as CRMs. Paleomagnetic vein contact tests show no direct correlation between either component and the veins, however, there appears to be a strong lithological control on the acquisition of the ChRM. Samples with higher porosity and permeability tend to contain more reliable magnetizations than samples with low porosity and permeability. Elevated ⁸⁷Sr /⁸⁶Sr data from the host matrix indicate that the rocks have been altered by fluids with a radiogenic signature. C/O isotopes of calcite veins show a wide range of light δ¹⁸O over a narrow range of δ¹³C, suggesting formation due to either a wide range of warm fluids or fluids with variable meteoric content. The geochemical results are consistent with the interpretation that the magnetite CRM formed as a result of the migration of hydrocarbons and/or evolved basinal fluids into the unit. The timing of remagnetization relative to folding suggesting acquisition due to fluid migration ahead of the deformation front. The pyrrhotite component is interpreted to be the result of thermal sulfate reduction, caused by warm fluids moving into the carbonates along faults and fractures. Fluid inclusion data along with sulfur characterization will be presented to investigate this issue.